The invention relates to a percussion drilling apparatus having a control unit.
In a known percussion drilling apparatus according to German Pat. No. 2,634,066, a control unit is provided with a control pipe which is axially non-displaceable in an end screw connection of the housing of the apparatus and possesses the compressed air feed, and on whose free end sits a control sleeve which is arranged non-rotatably with respect to the housing. The control pipe can be rotated in this and in the end screw connection. In the region of its free end, it has control orifices for reversing the forward and return flow of the apparatus, or vice versa, these orifices being capable of being brought into coincidence with corresponding orifices in the control sleeve. The control sleeve is provided with control orifices which are essentially adjacent to one another and interact with corresponding orifices in a percussion piston, which slides back and forth on this control sleeve and is displaceable in the housing of the percussion drilling apparatus, for controlling the piston either during its advance cycle or during its return cycle. Moreover, the orifices for the advance cycle and return cycle are arranged alternately one after the other, for example a return control orifice follows an advance control orifice, etc.
This alternate arrangement of advance control orifices and return control orifices has a very substantial disadvantage since this arrangement means that these control orifices and hence the entire displacement process can no longer be freely optimized. This is particularly important for ensuring that such percussion drilling apparatuses run reliably in a backward direction even when used in a vertical position. Furthermore, it is not possible to arrange seals to exclude stray air, which in some cases has a substantial adverse effect on the reversing processes and the displacement sequences. Moreover, this secondary air also results in substantial energy losses. The radial structure of the control unit also imposes restrictions in terms of the dimensions and hence the material cross-sections. This is particularly so in the case of small apparatuses. In connection with the flow behavior, which particularly in this case cannot be optimized, pronounced turbulence can occur in the region of the control orifices, which on the one hand has an adverse effect on the control processes and on the other hand has been found to lead to high vibration loads and therefore frequently to fractures in the control components of the apparatus.
A percussion drilling apparatus of a similar type, whose control differs from that described above only in the removal of the compressed air and in the method of fixing in the advance and return positions, is described in German Pat. No. 2,105,229. It therefore also has the above-mentioned disadvantages.